docs: def _AtildeTerm(N, h, m, k, dW, Km0, Pm0):
      """kth term in the sum for Atilde (Wiktorsson2001 p481, 1st eqn)"""
      M = m*(m-1)//2
      Xk = np.random.normal(0.0, 1.0, (N, m, 1))
      Yk = np.random.normal(0.0, 1.0, (N, m, 1))
      factor1 = np.dot(Km0, Pm0 - np.eye(m**2))
      factor1 = broadcast_to(factor1, (N, M, m**2))
      factor2 = _kp(Yk + np.sqrt(2.0/h)*dW, Xk)
      return _dot(factor1, factor2)/k